The present invention relates to a rotor for a hybrid type stepping motor and manufacturing method thereof.
Japanese Patent Application Laid-open Publication No. 270531/2000 shows a rotor for a hybrid type stepping motor, which comprises two stack assemblies and a rotor collar. The two stack assemblies each include a pair of rotor stacks having a plurality of small teeth arranged in a circumferential direction at their peripheral portions, and a permanent magnet which is held between the pair of the rotor stacks and is magnetized so that polarity of magnetic poles appearing at the small teeth of one of the paired rotor stacks may be different from that of magnetic poles appearing at the small teeth of the other rotor stack. Further, the two stack assemblies are mounted onto a rotating shaft so as to be arranged along the rotating shaft in an axial direction thereof. The rotor collar is made of a nonmagnetic material and is held between two adjacent stack assemblies so as to form a gap between the two adjacent stack assemblies. Then, the plurality of the small teeth at one of the paired rotor stacks are out alignment by ½ pitch with the plurality of those at the other rotor stack. The rotor collar is arranged inside depressed portions formed in the two rotor stacks opposed to each other in the axial direction of the rotating shaft with the the rotor collar disposed therebetween. Further, the plurality of the small teeth of one of two rotor stacks opposed to each other in the axial direction with the rotor collar disposed therebetween is also out of alignment by ½ pitch with those of the other rotor stack. In this rotor, the rotor stack is provided with a depressed portion that opens in the axial direction of the rotating shaft. Consequently, the rotor stack can be reduced in weight, thereby lessening the moment of inertia for the rotor.
Generally, in a rotor for a hybrid type stepping motor, a rotor assembly is constituted by combining a plurality of rotor stacks and one or more rotor collars by adjusting a plurality of small teeth in pitch misalignment. Then, the rotor assembly is press into a rotating shaft and fixed thereon. In the conventional rotor like this, however, when constituting the rotor assembly, position alignment of annular rotor collars and rotating shaft was impossible and it was therefore likely that both the axial centers of the both became out of alignment. Besides, there was such a trouble that a relative displacement in a radial direction of the rotating shaft occurred between the rotor stacks and the rotor collar. In the rotor like this, there is a possibility that it would become impossible to press the rotor assembly into the rotating shaft and the rotor collar would be unbalanced in weight in a circumferential direction of the rotating shaft.